[CB7Man]

My main question was what would be causing the speeduino to start cutting at around 5k rpms?

This frustration led me to go back to my original configuration. But now I want to give it another go.

Can you group all grounds together?
Is there a special ground for the 5v line?
Am I supposed to use shielded wires?

[PSIG]

My main question was what would be causing the speeduino to start cutting at around 5k rpms?

I would begin by posting a log of the issue, and the exact tune used to take it, as a ZIP file.

This frustration led me to go back to my original configuration. But now I want to give it another go.

What is different from original to now?

Can you group all grounds together? Yes. Example below.
Is there a special ground for the 5v line? No, we usually dedicate one ground terminal for all 5V grounds.
Am I supposed to use shielded wires? No, and are an item of last-resort. Find what is emitting EMI noise and fix that, preferably.

Note the WBO2 labels of H and S are Heater ground and Signal ground. Sensor grounds terminate at one point at the ECM. Power (high-current) grounds avoid this point. All control (ECM) grounds terminate as a "star" ground at a single point on the engine (typically the block). This is to avoid voltage offsets or ground loops between signal components and the processor, and to avoid using ECM ground wires to carry current to "balance" the grounds. In all cases, we try to avoid using ground wires that carry current for grounding signal components. Current affects signal accuracy.

[Rednaxs60]

Grounds can be the bane of one's existence.

Further to @PSIG post, grounding can play havoc with ECU function, engine sync and other aspects - had this issue with mine. All unused ECU ground connections must be tied to the main ECU main ground wire.

This video by Andy Whittle is good viewing. To test for ground issues with an ECU, disconnect the ECU from the wiring harness. Test for continuity between sensor ground(s) and main ECU ground wire at the wiring harness. Continuity, you have an issue, no continuity - good. Video web site: https://www.youtube.com/watch?v=EJ2TeodWDUE Check minute 7:46.

This video supports @PSIG premise that all grounds terminate at the same place. If the grounds on your vehicle do not terminate at the same place (use the frame), ensure that the essential engine parts/components and the ECU use the same engine ground point before the battery. Grounds that do not affect engine or ECU operation are not as critical.

You can also reroute "dirty", noisy grounds from the ECU grounding system. These are fuel pumps, rad fans; not many but could be enough to be annoying. The picture posted by @PSIG is a good example of using the engine as the main ground, but have the grounds connected at different spots. The engine block is a good noise filter between grounding points.

My Honda Goldwing 1200 FI model uses the wiring harness to direct the grounds to the motorcycle frame, then to the engine block, then to the battery. I have changed this so that the essential grounds go directly to the engine block, bypassing the frame, then to the battery. Wiring and connections degrade over time.

Will follow. Good luck.

[CB7Man]

Ok, makes sense. I had the o2 heater grounded at the ecu...I spent alot of time putting injection on my 79 kdx 400. Tuning was real nice, I could use my phone. But the breaking up made me rip it all out.
Someone told me "you can't do better than the engineers" now I'm getting the ambition to re install it as I miss the one kick start ups.

[Rednaxs60]

Definitely agree that the OEM design engineers have a leg up on us DIY users - they have better toys to play with to achieve the aim; however, you can get very close if not better with an aftermarket installation. Your install will be specific to your requirements, VE and spark table calibrations will be better suited for your application. The features/functions in the engine tuning software give the DIY engine tuner a lot of flexibility.

I have discussed engine timing on this forum. It was mentioned that the OEM spark tables are a balanced approach to engine timing. Your approach will be more focused on your requirements - advancing/retarding the timing to suit your riding profile, not the thousands of people who may buy the vehicle.

Remember that the OEM has to design and have a product that meets the requirements of the 30 KPH driver, or the 170 KPH driver, meet environmental legislation, and do this well. There are many aftermarket installations that meet and may exceed these government requirements. The caveat by an aftermarket ECU manufacturer that the product is only intended for off road use is a due diligence disclaimer. Time is the only factor that can inhibit you achieving your goals.

Don't be discouraged when something does not work as expected. These hiccups are a mystery that needs a solution.

I treat my project as if it were a complete working model. Define what I want to do in the next maintenance period (not too much), do the work, then ride the bike, repeat as required. The project will get done and to a high standard.

I mentioned that I have made a few oops along the way, learned from these and have progressed the project.

Good luck.